About one out of every eight adults is an "ex-Christian," a new survey reveals.

These include those who left the Protestant or Catholic tradition that they were a part of as a child and who now report being atheist, agnostic or some other faith, according to the Barna Group.

Meanwhile, those who switched from a non-Christian faith or non-belief (from their childhood) to Christianity as an adult represent three percent of the American population.

Findings are based on telephone interviews derived from a random sample of 2,004 adults in the U.S. The interviews were conducted in the fall of 2008 and summer of 2009. Participants were asked to identify their childhood faith and their current faith allegiance.

A second survey asked respondents if they had ever “changed to a different faith or significantly changed their faith views” or if they were “the same faith today as they were as a child.”

According to the Christian research group, the most common reasons for leaving Christianity included life experiences, such as gaining new knowledge or education; feeling disillusioned with church and religion; feeling the church is hypocritical; having negative experiences in churches; being in disagreement with Christianity about specific issues such as homosexuality, abortion or birth control; feeling the church is too authoritarian; wanting to express their faith outside of church; and searching for a new faith or wanting to experience other religions.

The top motivations for becoming a Christian, meanwhile, were going through difficult life events; getting older and seeing life differently; wanting to connect with a church and grow spiritually; discovering Christ; or wanting to know what was in the Bible.

The median age at which respondents changed their faith was 22. Sixty-eight percent of respondents had a major faith change before the age of 30.

David Kinnaman, president of the Barna Group and director of the research, emphasized the importance of "staying in tune with people’s questions and doubts."

"Clergy are typically older than those going through significant questions about their faith and are less likely to have personally experienced a period of major faith re-orientation themselves," he noted. "What's more, not every person goes through a crisis of faith, so individuals who are going through spiritual transitions often go unnoticed."

Overall, the Barna Group, based in Ventura, Calif. found that less than a quarter (23 percent) of respondents switched faith traditions – including those who switched between Catholicism and Protestantism but not including those who changed from one Protestant denomination to another.

Twelve percent of adults shifted affiliations within the Protestant tradition.

"The study underscores that the spiritual allegiances of childhood are remarkably sustainable in our society." said Kinnaman. "[T]he most common faith journey that people take is to form spiritual commitments as children and teenagers that typically last for the duration of their life."